1. Field of the Invention
The present invention relates to the field of ink jet printheads and associated ink delivering method, and more particularly, to a high-density ink jet printhead having a two-directional central ink flow channel and a one-directional periphery ink flow channel.
2. Description of the Related Art
Please refer to FIG. 1. FIG. 1 is a cross-sectional diagram of a prior art printhead 10. Structures similar to the printhead 10 are disclosed in U.S. Pat. Nos. 4,680,859 and 4,683,481 of Samuel A. Johnson and assigned to Hewlett-Packard Company. The printhead 10 comprises a central ink feed slot 12 formed at a center portion of a substrate 14. The ink feed slot 12 may be formed by sand blasting, laser cutting, or etching techniques. Heater resistors 16 are provided on both sides of the ink feed slot 12 for generating bubbles during an ink jet printing operation. An orifice plate 18 with a plurality of nozzles 22 formed therein is positioned on the substrate 14 and each of the nozzles 22 is positioned corresponding to one heater resistor 16. During an ink jet printing operation, ink will flow through the central ink feed slot 12 to chambers 24 between the orifice plate 18 and the substrate 14. The heater resistors 16 thereafter heat the ink flow into the chambers 24 to generate bubbles for pressurizing the ink, thereby forming an ink droplet 26.
Please refer to FIG. 2. FIG. 2 is a cross-sectional diagram of a prior art printhead 30. Similar structure is disclosed in U.S. Pat. No. 5,278,584 of Brian J. Keefe et al. and assigned to Hewlett-Packard Company. As shown in FIG. 2, the printhead 30 comprises a central ink slot 32 formed between a printhead cartridge 31 and a substrate 33. channels 34 are formed between the end of the central slot 32 and vaporization chambers 36. Each of the vaporization chambers 36 is provide with a thin film resistor 38 for generating a bubble. During an ink jet printing operation, ink from an ink reservoir (not shown) flows through the central slot 32 and split channels 34 to the vaporization chambers 36. When the thin film resistors 38 are energized, the ink within the vaporization chambers 36 is ejected, as illustrated by the emitted drops of ink 42.
Please refer to FIG. 3. FIG. 3 is another prior art printhead 50 disclosed in U.S. Pat. No. 6,010,208 of James Harold Powers et al. and assigned to Lexmark International Inc. Two rows of nozzles 54 are located one each side of a manifold 52 of the printhead 50. Ink flows through the central manifold 52 laterally to the chambers 56 corresponding to the nozzles 54.
Please refer to FIG. 4 and FIG. 5. FIG. 4 is a schematic diagram showing a prior art nozzle array of a color printhead 60. FIG. 5 is a schematic, cross-sectional view of an ink cartridge 70 having a printhead 60 of FIG. 4 mounted thereon. The ink cartridge 70 comprises three ink reservoirs 72 for storing ink of different colors such as yellow, magenta, and cyan. The printhead 60 includes a substrate with three ink slots 62 and a plurality of nozzles 64 arranged in six columns on an orifice plate 61. Each of the six columns of nozzles 64 is located on a side of the three ink slots 62 which are connected with associated ink reservoirs 72. Likewise, ink from the ink reservoirs 72 flows through the ink slots to the chambers and then splits into two flows in opposite directions. The heater resistors 66 then create ink bubbles to form drops of ink out of the nozzles 64. FIG. 6 is nozzle array of another prior art color printhead 80. Similarly, printhead 80 comprises six rows of nozzles 64 and three ink slots 62 (indicated by a dashed line). The difference between the printhead 60 and printhead 80 is the arrangement of the ink slots 62.
From above, ink from an ink reservoir is delivered either through a central ink feed slot or edge feed path (through an edge of a substrate). Unfortunately, the nozzles must be located near the ink slot, thus limiting the nozzle number of a printhead and resolution.
Accordingly, the primary objective of the present invention is to provide a printhead capable of delivering colors of ink simultaneously from a central path and an edge path.
Another objective of this invention is to provide an ink delivery method for increasing nozzle number in a unit area. Four or more columns of nozzles may be packed into a printhead having a smaller printhead surface, thereby improving its resolution.
Still another objective of this invention is to provide a printhead having a smaller size that is capable of printing three or more colors of ink.
Briefly, the printhead has a substrate, a nozzle layer, and a plurality of bubble generators. A plurality of first chambers and a plurality of second chambers are formed between the nozzle layer and the top of the substrate. A central ink flow channel and a periphery ink flow channel for delivering ink to the chambers are formed in the substrate. The characteristic of the present invention is that positioning the central ink flow channel and the periphery ink flow channel together on the substrate so that the amount of the nozzles per unit area of the printhead is increased.